What is DCIS? Contents. The breasts

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1 This information is an extract from the booklet Understanding ductal carinoma in situ (DCIS). You may find the full booklet helpful. We can send you a free copy see page 6. Contents The breasts What is DCIS? Risk factors and causes This information is about ductal carcinoma in situ, usually called DCIS for short. DCIS is the earliest possible form of breast cancer. DCIS is non-invasive. This means that breast cancer cells are in the milk ducts, but they haven t spread into (invaded) surrounding breast tissue. The breasts Breasts are made up of fat, supportive (connective) tissue and glandular tissue containing lobules. The lobules (milk glands) are where breast milk is made. They connect to the nipple by a network of fine tubes called ducts. The breast tissue extends into the lower armpit (axilla). The armpits also contain a collection of lymph nodes (glands), which are part of the lymphatic system. The lymphatic system protects you from infection and disease. It is a network of lymph glands throughout the body connected by tiny vessels called lymph vessels. Questions about cancer? Ask Macmillan Page 1 of 6

2 Side view of the breast Rib Muscle Fatty tissue Lobe Milk duct Nipple It s common for a woman s breasts to be a different size or shape from each other. They also feel different at different times of the month. For example, just before a woman s period, her breasts may feel lumpy. As a woman gets older, her breasts may change size and shape, and become softer. What is DCIS? To understand DCIS, it helps to know how cancer usually develops. The organs and tissues of the body are made up of tiny building blocks called cells. Normally, cells divide in an orderly and controlled way. But if the process gets out of control, the cells carry on dividing and develop into a lump called a tumour. Doctors can tell whether a tumour is benign (noncancerous) or malignant (cancerous) by removing a piece of tissue (biopsy) and examining a small sample of cells under a microscope. Normal cells Cells forming a tumour Page 2 of 6 Questions about cancer? Ask Macmillan

3 Breast cancers usually start in the cells that line the lobules and their draining milk ducts (see diagram on page 2). The place where DCIS starts is the terminal duct lobular unit. In this information, we use the simpler terms lobules and ducts. In DCIS, the cancer cells are completely contained in the lobules and ducts. The cells haven t broken through the walls of the lobules or ducts or grown into surrounding breast tissue. Side view of the breast showing DCIS Rib Muscle Fatty tissue Lobe Invasive cancer Nipple Localised DCIS DCIS is the earliest possible form of breast cancer. It isn t a life-threatening condition, but treatment is usually recommended. DCIS was something I d never heard of before. Different friends have had different sorts of breast cancers but never DCIS. Sue Questions about cancer? Ask Macmillan Page 3 of 6

4 DCIS and invasive breast cancer If DCIS isn t treated, it may over time spread into (invade) the breast tissue surrounding the ducts to become an invasive breast cancer. Not every untreated DCIS will develop into an invasive breast cancer. But breast specialists may advise treating DCIS because it isn t possible to tell for certain which individual cases of DCIS will become an invasive cancer. Having DCIS means you have a slightly higher risk of getting cancer elsewhere in the same breast or in your other breast. Guidelines recommend that women who have had DCIS have mammograms every year. Risk factors and causes The risk factors for DCIS and invasive breast cancer are similar. DCIS can occur in both women and men, but it is rare in men. We have more information specifically about breast cancer in men. It s not clear exactly what causes breast cancer but different things can increase a woman s risk of developing it. These include: Increasing age The risk of DCIS increases with age. It s rare in women under the age of 35. Previous breast cancer and some non-cancerous (benign) breast conditions Having one of these can increase the risk. Dense breast tissue Women are slightly more likely to develop cancer when the breasts have more glandular and connective tissue, with very little fatty tissue. Not having children Women who haven t had children are slightly more likely to develop breast cancer than women who have. Not breastfeeding Women who have never breastfed are slightly more at risk than women who have breastfed for more than a year. Early periods or a late menopause Women whose periods started before they were 12 or who ve had a late menopause (after the age of 50) are at a slightly higher risk. Page 4 of 6 Questions about cancer? Ask Macmillan

5 Hormone replacement therapy (HRT) This reduces some effects of menopause but can increase the risk of breast cancer. You can talk to your GP about the benefits and possible risks of taking HRT. Lifestyle factors Being overweight after the menopause and drinking more than two units of alcohol a day over many years can slightly increase risk. Smoking heavily from a young age can also increase risk. Family history and risk Most women diagnosed with breast cancer don t have any family history of it. Only a very small number of women with breast cancer have a gene that greatly increases the risk of breast cancer. The two genes most often found in hereditary breast cancer are called BRCA1 and BRCA2. Generally, the chance of breast cancer being hereditary is greater when: a number of family members have been diagnosed with breast cancer or related cancers, such as ovarian cancer these family members are closely related to you these family members were diagnosed at a young age. Online risk assessment Our website has an interactive tool called OPERA (Online Personal Education and Risk Assessment). It asks specific questions about your family history of breast and ovarian cancer. It gives you personalised information and support about your inherited breast cancer risk. OPERA isn t intended to take the place of professional genetic counselling services. If you re concerned about genetic risk, you should still consult your doctor. You can access OPERA at macmillan.org.uk/opera Questions about cancer? Ask Macmillan Page 5 of 6

6 More information and support More than one in three of us will get cancer. For most of us it will be the toughest fight we ever face. And the feelings of isolation and loneliness that so many people experience make it even harder. But you don t have to go through it alone. The Macmillan team is with you every step of the way. To order a copy of Understanding ductal carcinoma in situ (DCIS) or any other cancer information, visit be.macmillan.org.uk or call We make every effort to ensure that the information we provide is accurate and up to date but it should not be relied upon as a substitute for specialist professional advice tailored to your situation. So far as is permitted by law, Macmillan does not accept liability in relation to the use of any information contained in this publication, or thirdparty information or websites included or referred to in it. Macmillan Cancer Support Registered charity in England and Wales (261017), Scotland (SC039907) and the Isle of Man (604). Registered office 89 Albert Embankment, London, SE1 7UQ REVISED IN APRIL 2015 Planned review in 2017 Page 6 of 6 Questions about cancer? Ask Macmillan